Regarding a fuser unit that is used in an image forming apparatus of an electrophotographic method, it is known that a fuser unit of which a heat source (heat generator) such as halogen lamp, a thermistor (temperature detecting member) and the like are arranged at the inside of a belt (cylindrical member) made of a heat-resistant film (for example, refer to FIG. 6 of JP-A-04-122969). In the fuser unit, the heat generator is controlled based on temperatures detected by the temperature detection unit, so that a fixing temperature and the like are controlled.